docs: def integ(self,n=1,x0=None):
          """ Compute *n*-th indefinite integral of ``self``.
  
          If *x0* is specified, then the definite integral,
          integrating from point *x0*, is returned.
  
          :param n: Number of integrations.
          :type n: integer
          :param x0: Starting point for definite integral (optional).
          :returns: *n*-th integral of ``self``.
          """
          if n==1:
              if self.order<0:
                  ans = PowerSeries([0])
              else:
                  ans = PowerSeries([0.*self.c[0]] +
                      [x/(i+1.) for i,x in enumerate(self.c)])
              if x0 is not None:
                  return PowerSeries([ans.c[0]-ans(x0)]+list(ans.c[1:]))
              else:
                  return ans
          elif n>1:
              return self.integ().integ(n=n-1, x0=x0)
          elif n==0:
              return self